Natural gas which is mostly methane is an abundant and relatively inexpensive natural resource for fuel and chemical feed stock. Methane is a thermally stable molecule, and its partial oxidation is difficult because of the ease of complete oxidation of the partial oxidation products. The method of this invention makes it possible to partially oxidize methane to methanol, formaldehyde, and other useful chemical products. The availability of lattice oxygen of complex metal-oxide compounds is critical to such reactions.
In FIG. 1, there is shown a schematic diagram of a solid electrolyte cell for oxidation of methane. The cell includes a solid electrolyte member 11 with two porous film electrodes 12 and 13, deposited on the two surfaces of the solid electrolyte member 11. The electrode 12 is exposed to an oxygen-containing gas such as air or pure oxygen and serves as the cathode. The anode is in contact with a fuel; for example, methane. The cell generates an electrical potential in accordance with the Nernst equation, ##EQU1## where R is gas constant, T is temperature, F is Faraday's constant and P.sub.O.sbsb.2.sup.II is the partial oxygen pressure on the cathode side (0.214 for air) and P.sub.O.sbsb.2.sup.I is the partial oxygen pressure on the fuel side. The fuel is oxidized at the anode and provides the energy. An electrochemical cell of this type is described in U.S. Pat. No. 4,459,340.
Eng and Stoukides, Catal. Rev.-Sci. Eng., 33(3&4), 381 (1991) have reviewed the use of a solid electrolyte cell, such as that described above, for the cogeneration of electrical energy and useful chemicals. While noble metals have intrinsic catalytic activity for oxidation of methane, they favor complete oxidation to carbon dioxide and water.
In related research, Wise and McCarty have shown that complex oxides with perovskite structure can be used as a catalyst in the complete oxidation of methane. [Wise, H. and McCarty, J. G.; Perovskite Catalysts for Methane Combustion, Catalysis Today (1990) 231-248, Elsevier Science Publishers, B. V. Amsterdam.]